#include<bits/stdc++.h>
using namespace std;
int main()
{
int n=100,i=1,s=0;
while(n>=1){
	s+=n;
	n-=3;
} 
cout<<s;

	return 0;
}

/**************************************************************
	Problem: 1053
	User: zy002
	Language: C++
	Result: Accepted
	Time:4 ms
	Memory:2072 kb
****************************************************************/